Composition containing aziridino groups, method of production and use thereof

ABSTRACT

The invention relates to a composition comprising a prepolymer as component (A), wherein the prepolymer comprises aziridino groups and is characterized by an equivalent weight EW1, a crosslinker as component (B), wherein the crosslinker has a structure being different from the structure of the prepolymer and comprises at least three 2-alkyl-substituted aziridino groups and is characterized by an equivalent weight EW2, an initiator as component (C) being able to start curing of the composition, optionally filler(s) as component (D) and optionally additive(s) as component (E), wherein equivalent weight is defined as (molecular mass of the molecule)/(number of aziridino groups present in the molecule) and wherein EW1&gt;EW2. The invention also relates to the use of the composition for coating, sealing, molding, adhering, making impressions, producing a dental material.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a national stage filing under 35 U.S.C. 371 of PCT/US2007/070057, filed on May 31, 2007, which claims priority to European Patent Application No. 06011708.2, filed on Jun. 7, 2006, the disclosure of which is incorporated by reference in its entirety herein.

FIELD

The invention relates to a composition comprising a prepolymer with aziridino groups as component (A), a crosslinker with at least three 2-alkyl-substituted aziridino groups as component (B) and an initiator capable of starting the curing of the composition as component (C). The composition can be used in the dental field, e.g. as dental impression material.

BACKGROUND

Due to their chemical nature, polyethers are inherently hydrophilic and are a well-recognized class of materials, especially for dental applications. Polyether groups containing compositions and their use in the dental field are also the subject of several patent applications.

US 2004/0014924 A1 relates to silicone based aziridino compounds. The materials described show functionality of at least two aziridino groups in the average molecule having a prepolymeric structure. The general formula shows structures with aziridino functions pendant from a silicone backbone.

US 2004/0014907 A1 describes linear and branched prepolymeric silicones bearing terminal and/or pendant aziridino moieties and curable compositions made thereof.

WO 2004/014323 A1 relates to monofunctional aziridine compounds which can be used to enhance speed of cure. The addition of monofunctional aziridine compounds to a given concentration of aziridine compounds with at least two aziridine rings enhances speed of cure.

Other publications that mention the use of aziridines include e.g. WO 92/19655 A1, U.S. Pat. No. 5,164,467 A1 and U.S. Pat. No. 4,605,698 A1.

So far, achieving a sufficient tensile strength value of the compositions described above has not been subject of intensive investigations. Some of the compositions, however, might lack sufficient tensile strength thus risking rupture of thin parts of material when the set impression is removed from the mouth or a plaster model is removed from the impression.

Thus, there is a need for a composition having improved properties.

SUMMARY OF THE INVENTION

It might be advantageous to provide a polyether composition with improved tensile strength properties by adding to existing formulations an additive that is able to modify the network structure, as opposed to developing an entirely new formulation.

However, simply adding further components to an existing composition might cause other drawbacks in view of the fact that compositions containing aziridino groups cure in a quite complex manner. For example, in aziridino polymerization, ring formation of di- and oligomerization is a well known side reaction which becomes pronounced with high functional group density (Encyclopedia of Polymer Science and Engineering Vol. 1, p698ff, Wiley 1985 ISBN: 0-471-89540-7 (v.1)).

Commercially available trifunctional aziridino monomers like TTMAP, TTAP or PTAP (R. R. Roesler, K. Danielmeier, Progress in Organic Coatings 50 (2004) 1-27) on the one hand might be highly functional and have a low aziridino equivalent. On the other hand, however, these substances have very low molecular weights which can result in insufficient crosslinking because of the high functional density of these substances.

Moreover, simply increasing the aziridino functionality of some of the components of the composition combined with an appropriate alteration of the initiating system often results in a more or less significant acceleration of cure.

In the dental field the curing behaviour of impression materials is characterized by the working time and the setting time. The working time is defined according to DIN EN ISO 4823:2000. The setting time is defined as the time until the cured elastomer shows a recovery after deformation of at least 96.5% as measured according to DIN EN ISO 4823:2000 and a strain in compression within the limits of DIN EN ISO 4823:2000.

While a reduced setting time alone would be desirable, acceleration often is accompanied with a shortened working time, which may be unsuitable for certain dental procedures.

Various embodiments of the present invention take the above issues into account and provide curable compositions with improved mechanical properties, especially in regard to tear strength and/or elongation at break.

In some implementations of the invention, it might be advantageous if this improved tensile strength and/or elongation at break can be achieved without a negative effect on other physical properties such as e.g. Shore hardness.

Thus, in one embodiment, the invention features a composition comprising:

-   -   a) a prepolymer as component (A), wherein the prepolymer         comprises aziridino groups and is characterized by an equivalent         weight EW1,     -   b) a crosslinker as component (B), wherein the crosslinker has a         molecular structure being different from the structure of the         prepolymer and comprises at least 3 2-alkyl-substituted         aziridino groups and is characterized by an equivalent weight         EW2,     -   c) an initiator as component (C) being able to start curing of         the composition,     -   d) optionally filler(s) as component (D) and     -   e) optionally additive(s) as component (E),         wherein equivalent weight EW is defined as (molecular mass of         the molecule)/(number of aziridino groups present in the         molecule) and wherein EW1>EW2.

The invention also relates to a kit of parts comprising

-   -   Part I comprising component (A) and component (B) and optionally         component (D) and/or component (E) and     -   Part II comprising component (C) and optionally component (D)         and/or component (E).

Moreover, the invention relates to a process for producing the composition comprising the step of mixing component (C) with components (A) and (B).

In addition the invention also relates to the use of the composition for coating, sealing, moulding, adhering, making impressions or producing a dental material.

Furthermore, the invention relates to the use of component (B) for increasing the tear strength and/or elongation at break of a polyether groups containing composition.

DEFINITIONS

A “prepolymer” in the context of the invention is defined as a compound or a mixture of compounds obtainable by polymerization (such as e.g. polycondensation reaction) of monomers resulting in an intermediate product or mixture of products with increased molecular weight compared to the monomers used. The resulting intermediate product itself bears functional groups (either left over from the initial polymerization or introduced afterwards). The prepolymer containing functional groups can be used for further polymerization reactions (such as e.g. polycondensation reaction or polyaddition reaction) leading to a polymer or polymer mixture with increased molecular weight compared to the prepolymer.

The term “crosslinker” refers to compounds being able to react with the functional group or groups on other compounds, prepolymers or polymer chains to lengthen them and connect them, e.g., to form a crosslinked network characteristic like that of a cured silicone elastomer. In contrast to a thermoplastic polymer, (i.e., a polymer that softens and flows upon heating) a crosslinked polymer, after crosslinking, is usually incapable of further flow. Cross-linked polymers differ in some important respects from linear and branched polymers. For example they swell in good solvents to form a gel but do not dissolve to form a solution. At elevated temperature, cross-linked polymers behave like soft but elastic solids rather than viscous liquids.

“Aziridines” in the context of the invention are a group of organic compounds sharing the aziridine functional group which is a three membered heterocycle with one amine group and two methylene groups. The parent compound of the aziridines is called aziridine with molecular formula C₂H₅N.

An “alkyl-substituted aziridino group” in the context of the invention is an aziridine group, wherein at least one of the hydrogen atoms of the methylene groups is substituted by an alkyl group, preferably by an C1 to C4 alkyl group, e.g. methyl, ethyl, n- and iso-propyl or n-, iso- or tert.-butyl group. In the chemical literature a “methyl substituted aziridine” is sometimes also referred to as “propylene imine”.

“Equivalent weight” (EW) in the context of the invention is defined as (EW)=(molecular weight of the respective molecule)/(number of aziridino groups in the molecule).

The equivalent weight reflects the “density” of aziridino groups in the respective molecule. The lower the value of EW, the more aziridino groups are present in the molecule. The aziridino groups present in component (A) usually take part in the crosslinking reaction with crosslinker component (B).

For molecules having a low molecular weight, the number of aziridino groups can be counted. For molecules having a higher molecular weight the equivalent weight (EW) can be determined by titration of the aziridino groups and determination of the molecular weight of the respective molecule, prepolymer or polymer.

“Molecular weight” in the context of the invention and if not otherwise indicated always means number average molecular weight (M_(n)).

The molecular weight (M_(n)) of the polymerizable compound before setting can be determined using nuclear magnetic resonance spectroscopy (end-group determination). In this respect proton (¹H) NMR techniques are employed to estimate the molecular weight of the precursor of the prepolymer. Integrated signals of the terminal —CH₂— groups are compared to the integrated sum of proton signals from backbone hydrocarbon protons taking into account co-monomer ratio, if applicable. To achieve appropriate separation of terminal methylene proton signals from the backbone proton signals, terminal hydroxyl groups are esterified with trifluoroacetic acid.

“Polyethers” in the context of the invention are compounds having a molecular weight of at least about 500 and containing in the backbone at least about 5 ether moieties (i.e. any of a class of organic compounds that have two hydrocarbon groups linked by an oxygen atom). Polyethers are frequently used in the dental field as impression materials. Polyether groups containing compositions used as dental impression material can be cured by different mechanisms. One widely used mechanism is the curing caused by the reaction of aziridino groups with each other.

Examples of polyether groups containing impression materials are given in U.S. Pat. No. 5,569,691 (3M ESPE), US 2004/0146713 A1 (HeraeusKulzer), US 2006/0069180 (Kettenbach) and U.S. Pat. No. 5,526,134 (Ivoclar). Commercially available materials are sold e.g. under the brand Impregum™ (3M ESPE).

The term “dental materials” comprises impression materials, such as precision impression materials, situation impression materials, bite registration materials, duplicating materials (applicable for the duplication of master models, e.g. for all-ceramic restorations requiring a refractory investment model and when inlays, onlays, cantilevers and other precision attachments are being fabricated) and modelling materials (applicable for e.g. reconstructing the gingival, producing crowns and bridges). Duplicating and modelling materials are commercially available e.g. from 3M ESPE AG under the trademarks Reprogum™ or Vestogum™.

The terms “comprises” and variations thereof do not have a limiting meaning where these terms appear in the description and claims.

As used herein, “a”, “an”, “the”, “at least one” and “one or more” are used interchangeably. Thus, for example, a dental composition that comprises “a” aziridine group containing prepolymer can be interpreted to mean that the prepolymer includes “one or more” aziridine groups. Similarly, a composition comprising “a” filler can be interpreted to mean that the composition includes “one or more” types of fillers.

As used in this specification and the appended claims, the term “or” is generally employed in its sense including “and/or” unless the content clearly dictates otherwise.

Also herein, the recitations of numerical ranges by endpoints include all numbers subsumed within that range (e.g., 1 to 5 includes 1, 1.5, 2, 2.75, 3, 3.80, 4, 5, etc.).

DETAILED DESCRIPTION

The invention provides a means for improving mechanical properties like tear strength and/or elongation at break of curable materials like polyether groups containing compositions.

It was found that the addition of certain crosslinkers comprising at least three 2-alkyl-substituted aziridino groups to prepolymers with aziridino groups in the presence of a suitable initiator results in a composition with improved tear strength and/or elongation at break compared to a composition not containing these crosslinkers.

If the set composition has a high elongation at break value, tear strength is not the only property to avoid ruptures of thin parts of material. The higher the value of elongation at break is, the lower is the risk of a rupture of thin parts of material.

For some applications a high hardness can be desirable. For precision impression materials hardness can be important when used with a dental tray that does not support the material. Commonly used trays not supporting the impression material are e.g. dual arch trays. In addition bite registration materials sometimes also should have a high hardness. Hardness is commonly measured as Shore hardness A. A Shore hardness A value of at least about 40 after 24 h is often considered as sufficient.

In a preferred embodiment the Shore hardness A value of the set composition of the invention is not negatively influenced by the addition of the crosslinker.

In one embodiment the prepolymer can be characterized by at least one of the following features:

-   -   Molecular weight     -   Molecular structure     -   Number of aziridino groups     -   Equivalent weight (EW1).

The molecular weight of the prepolymer usually is in the range of about 3,000 to about 12,000 or in the range of about 4,000 to about 10,000, or in the range of about 5,000 to about 8,000.

The prepolymer preferably has a linear molecular structure. The prepolymer typically comprises a linear backbone, which typically is end-capped with aziridino groups. Usually, there are no side chains pending from the backbone.

In one embodiment, the prepolymer is a hydrophilic groups, e.g. polyether groups containing prepolymer.

The prepolymer usually has an equivalent weight (EW1) of at least about 1,000, typically of at least about 3,000 or at least about 5,000.

The equivalent weight (EW1) usually does not exceed values of about 6,000 or about 10,000 or about 15,000.

Depending on the chemical nature and structure of the prepolymers chosen, different ranges for EW1 can be preferred.

Suitable ranges for EW1 are e.g. about 1,500 to about 4,000 or about 4,000 to about 10,000 or about 10,000 to about 15,000.

The prepolmyer can comprise at least about 2, 3, 4, 5 or 6 aziridino groups.

The prepolymer can be used in an amount of at least about 10 wt.-% or at least about 30 wt.-% or at least about 40 wt.-% with respect to the whole composition.

The prepolymer can be used up to an amount of at least about 90 wt.-% or at least about 80 wt.-% or at least about 70 wt.-% with respect to the whole composition.

Especially N-alkyl aziridine polyether containing compounds can be used and vulcanized in the presence of the initiator. The aziridine groups containing compound comprises at least two ethylene imine groups. However, more than two aziridine groups can be present, if desired.

Those components are know and described e.g. in U.S. Pat. No. 3,453,242 or U.S. Pat. No. 5,569,691 or U.S. Pat. No. 6,383,279 B1. These documents, especially as regards their disclosure on aziridine groups containing compounds is explicitly mentioned and herewith incorporated by reference.

The aziridine groups can be attached to an oligomeric and/or polymeric hydrocarbon, ester or ether backbone. The attached aziridine group can be represented by the formula

wherein R represents H, C₁-C₁₂ alkyl, C₂-C₁₂ alkenyl, C₂-C₁₂ alkinyl, C₇-C₁₅ alkylaryl, C₇-C₁₅ arylalkyl or C₃-C₁₂ cycloalkyl, and wherein hydrogen atoms can be replaced by Cl or F and/or wherein up to about 5 carbon atoms may be replaced by atoms or group of atoms selected from O, CO, N or S, E represents a C₁-C₁₈ branched or unbranched hydrocarbon chain wherein up to about 5 carbon atoms can be replaced by atoms or group of atoms selected from O, CO, N or S, G represents a group selected from C(O)O, C(O)NR, C(O), C(O)C(O), C(O)(CH₂)_(m)C(O) with m=1 to 10, C(S)NR or CH₂, L represents O, S or NR, with x=0 or 1.

In some embodiments the prepolymer according to the invention does not contain silicone moieties.

In another embodiment the crosslinker can be characterized by at least one of the following features:

-   -   Molecular weight     -   Molecular structure     -   Number of aziridino groups     -   Equivalent weight (EW2).

The molecular weight of the crosslinker is usually in the range of about 400 to about 10,000 or in the range of about 450 to about 4,000 or in a range of about 1,000 to about 8,000.

In specific embodiments, a certain molecular weight can be advantageous to reduce functional density of reactive groups in order to ensure a high degree of conversion.

A molecular weight in excess of 500 or 1,000 can be advantageous in terms of sensory perception as a high molecular weight reduces undesirable taste of such ingredients.

Low polarity and especially low water solubility can be advantageous, too, both for high degree of conversion and sensory properties. In this respect it can be desirable to use defined structures or mixtures of those rather than prepolymerically distributed mixtures of monomers. The latter often comprise a certain content of rather low molecular constituents that might have high polarity and high water solubility although overall molecular weight is well above 1,000. High molecular weight together with the desired multifunctionality is limited by considerations as regards stability and viscosity of the compound.

The crosslinker has a molecular structure being different from the molecular structure of the prepolymer. The crosslinker usually does not have a linear structure, but a branched structure, i.e. the crosslinker can comprise a backbone with side chains, some of the side chains bearing aziridino groups. The crosslinker molecules are typically defined molecules or simple mixtures of those but not prepolymeric distributed mixtures.

The backbone can comprise hydrophobic elements such as linear or branched aliphatic or cyclo aliphatic moieties (e.g. C₂ to C₁₂ moieties) and/or silicone moieties (linear, branched or cyclic). The backbone, however, can comprise hydrophilic elements such as ether or polyethers, as well.

The crosslinker comprises at least about 3, 4, 5, 6, 7, 8, 9 or 102-alkyl-substituted aziridino groups. Suitable alkyl substituents include C1 to C4 alkyl groups.

The crosslinker usually has an equivalent weight (EW2) of at least about 100, preferably of at least about 110 or at least about 125 or at least about 150.

The equivalent weight (EW2) usually does not exceed values of about 600 or about 800 or about 1,300.

Depending on the chemical nature and structure of the crosslinker chosen, different ranges for EW2 can be preferred.

Suitable ranges for EW2 are e.g. about 100 to about 500 or about 100 to about 900 or about 500 to about 1,300.

The crosslinker can be used in an amount of at least about 0.1 wt.-% or at least about 0.5 wt.-% or at least about 1 wt.-% with respect to the whole composition.

The crosslinker can be used up to an amount of at least about 20 wt.-% or at least about 15 wt.-% or at least about 10 wt.-% with respect to the whole composition.

The alkyl-substituted aziridino group containing crosslinkers can by synthesized by adding several alkyl-substituted aziridino functions to a molecular backbone. This can be done by various chemical procedures.

One way is e.g. to add alkyl-substituted aziridine to the double bonds of polyfunctional acrylates.

Another way is to use polyvalent alcohols or amines. These can be transformed into chloro oxalates or chloro formiates which can be reacted with protic aziridino derivatives like e.g. methyl-aziridino ethanol or other hydroxy- and amino functional aziridino derivatives.

In some cases it can be preferred to use activated amides as intermediates like imidazolides.

There are numerous other methods known to the persons skilled in the art that are described for instances in: O. C. Dermer, G. E. Ham, “Ethylenimine and other Aziridines” therein especially S. 106-205 as well as S. 340-393, Academic Press 1969 or R. R. Roesler, K. Danielmeier “Progress in Organic Coatings” 50 (2004) 1-27.

As starting material a molecular backbone can be used comprising a multitude of at least two hydroxy- or primary or secondary amino functions that are available for acylation. The molecular backbone can be taken from a wide variation depending on how introduction of the alkyl-substituted aziridino groups should be facilitated. Useful backbones include:

-   -   Silicones backbones can be useful, preferably functional         derivatives of D₄, D₅, D₆, M₄Q, M₃T, M₂; functional derivatives         are e.g. carbinols or carbamines; the terms “D₄, D₅, D₆, M₄Q,         M₃T, M₂” are well known terms to the skilled person in the art         working in the field of silicones.     -   Organic backbones, preferably aliphatic like glycerol,         trimethylol ethane or -propane, pentaerythritol or the         corresponding dimers via ether bridge, linear or cyclic sugar         alcohols like erythritol, sorbitol, mannitol or inositol,         aliphatic polyvalent primary or secondary amines like etylene         diamine derivatives, piperazine, tris-(aminoethyl)amine         derivatives.

To these backbones aziridino functions can be connected via acyl groups. The acyl groups can be part of carbonic ester, carbonic amide, carbonate, carbamate or urea groups.

The carbonic esters and amides, which can be used, comprise aliphatic acids ranging from acetic up to undecanoic acids, covering the readily available isomers of the intermediate chain lengths. The aziridino function there is usually attached by addition of an NH or OH moiety on an activated double bond or by substitution of a halide substituent.

The alkyl-substituted aziridino function can be attached to the acyl function using aziridino functional compounds like:

Crosslinkers which can be used are e.g.:

Compound 1:

M=467.6; Functionality: 3; EW2=156; 3-(2-Methyl-aziridin-1-yl)-propionic acid 2,2-bis-[3-(2-methyl-aziridin-1-yl)-propionyloxy-methyl]-butyl ester

Compound 2:

M=1709.1; Functionality: 3; EW2=570

Compound 3:

M=796.0; Functionality: 5; EW2=159

Compound 4:

with n=1 to 50, 1 to 30, 1 to 20 or 1 to 10; M=599.8 (for n=1); Functionality: 3; EW2=200 (for n=1) Compound 5:

with n=1 to 50, 1 to 30, 1 to 20, or 1 to 10; M=1193.3 (for n=1); Functionality: 4; EW2=298 (for n=1) Compound 6:

with n=1 to 50, 1 to 30, 1 to 20, or 1 to 10; m=11 to 50, 1 to 30, 1 to 20 or 1 to 10; M=1085.5 (for n=1 and m=1); Functionality: 4; EW2=271 (for n=1 and m=1) Compound 7:

with n=1 to 10, 1 to 8, 1 to 5 or 1 to 3; M=1265.9; Functionality: 4 (for n=1); EW2=316.2 Compound 8:

with n=1 to 10, 1 to 8, 1 to 5 or 1 to 3; M=1304; Functionality: 4 (for n=1); EW2=326 Compound 9:

with n=1 to 10, 1 to 8, 1 to 5 or 1 to 3; M=1092; Functionality: 4 (for n=1); EW2=273

Another suitable commercially available crosslinker component is:

Compound 10:

XAMA™-220 (TTMAP), Trimethylolpropane tris(3-aziridinopropionate), CAS #52234-82-9

M=467.6; Functionality: 3; EW2=156

The curable composition of the invention also comprises an initiator as component (C) being able to start curing of the composition. Useful initiators are e.g. sulfonium salts, especially alkyl sulfonium salts or sulfonium salts derived from glutaconic acid. Those and others are described e.g. in EP application number 05016531.5 or U.S. Pat. No. 4,167,618, the content of which in regard to initiators is explicitly mentioned and herewith incorporated by reference.

The initiator can be used in an amount of at least about 1 wt.-% or at least about 2 wt.-% or at least about 3 wt.-% with respect to the whole composition.

The initiator can be used up to an amount of at least about 30 wt.-% or at least about 20 wt.-% or at least about 10 wt.-% with respect to the whole composition.

In addition the curable composition of the invention may comprise filler(s) as optional component (D) and/or additive(s) as optional component (E).

A wide variety of inorganic, especially hydrophobic fillers may be employed such as silicas, aluminas, magnesias, titanias, inorganic salts, metallic oxides and glasses. It has been found to be possible to employ mixtures of silicone dioxides, including those derived from crystalline silicone dioxide, such as pulverized quartz (4 to 6 μm); amorphous silicone dioxides, such as a diatomaceous earth (4 to 7 μm); and silanated fumed silica, such as Cab-o-Sil TS-530 (160-240 m²/g), manufactured by Cabot Corporation. Varying the sizes and surface areas of the foregoing materials enables one to control the viscosity and thixotropicity of the uncured as well as the physical properties of the cured compositions. Some or all of the foregoing hydrophobic fillers may be surface treated with one or more silanating agents, as known to those of ordinary skill in the art. Such silanating may be accomplished, e.g., using known halogenated silanes or silazides. Some useful functionalized silicas are commercially available, e.g. products sold under the brands Aerosil™ (Degussa) or HDKH™ (Wacker).

Among the fillers which can be used are non-reinforcing fillers such as quartz, cristobalite, calcium silicate, diatomaceous earth, zirconium silicate, montmorillonite such as bentonite, zeolite, including molecular sieves such as sodium aluminium silicate, metal oxide powder such as aluminium or zinc oxide or their mixed oxides, barium sulphate, calcium carbonate, plaster, glass and plastic powder. The non-reinforcing fillers can be surface treated. The surface treatment can generally be carried out with the same methods as described for the reinforcing fillers.

Suitable fillers also include reinforcing fillers such as e.g. pyrogenic or precipitated silicic acid and silica aluminium mixed oxides. The above mentioned fillers can be hydrophobized, e.g. by treatment with organosilanes or siloxanes or by the etherification of hydroxyl groups to alkoxy groups. One type of filler or also a mixture of at least two fillers can be used. The particle distribution is preferably chosen such that there are no fillers with particle sizes of more than 50 μm.

A combination of reinforcing and non-reinforcing fillers can be desirable. In this respect, the quantity of reinforcing fillers may range from about 0.1 to about 15 wt.-%, in particular from about 1 to about 10 wt.-%. The difference in the named overall ranges, i.e. about 9 to about 80 wt.-%, can be accounted for by non-reinforcing fillers.

As the filler (D) is an optional component, it may not be present at all, but typically it can be present in the composition at an amount of from about 0 to about 80 wt.-%, or about 5 to about 70 wt.-%, or about 6 to about 60 wt.-% with respect to the whole composition.

Non-acidic fillers are preferred.

Besides filler (D) additives (E) can be present like dyes, pigments, thixotropic agents, flow improvers, polymeric thickeners, surfactants, odorous substances, diluting agents and/or flavourings. All kinds of known and compatible softeners and rheology modifiers like non reactive polymeric fluids or fats commonly used in commercialized impression materials can be added as well as pigments and stabilizers of any kind.

Preferred are those ingredients and additives that do not add unpleasant smell or taste. Compounds that have an unpleasant smell might be removed by thinfilm evaporation, if needed.

Suitable thixotropic agent(s) which can be added to the composition of the invention are organic compounds e.g. waxes according to the definition in Ullmanns Enzyklopädie der technischen Chemie, 4. Auflage, Verlag Chemie, Weinheim, Band 24, page 3 or triglycerides as described in U.S. Pat. No. 6,127,449. In general all organic non-water based thixotropic agents are suitable. That means that suitable thixotropic agents can alter the rheology especially of non-water based formulation.

Some of the untreated or surface treated inorganic fillers mentioned above may also contribute to the rheological properties of the formulation. Other thixotropic agents selected from the group of inorganic fillers are modified or unmodified bentonite(s), kaoline(s) and the like.

Suitable surfactant(s) are e.g. polyethers and polyether type materials with special structures such as Pluronic™, Synperonic™, Silwet™ type materials. Especially useful are substances described in U.S. Pat. No. 5,569,691 A1 the disclosure of which especially in regard to surfactants is herewith incorporated by reference.

Suitable diluting agent(s) usually do not contain reactive moieties like —SH or —COOH, primary or secondary amino groups, but may contain —OH. Liquids such as C₁₂-C₁₅ alkyl acetates, liquid derivatives of citric acid, esters of phthalic acid with branched alcohols like bis(2-ethylhexyl)phthalate or polymeric phthalates, C₂-C₁₈ bis(alkyl)esters of C₂-C₆ dicarboxylic acids like dioctylmaleate, dioctyladipate, aromatic and aliphatic esters of sulfonic acids like Mesamoll™, aromatic and aliphatic amides of sulfonic acides like N-ethyl toluene solfonic acid amide or N-butyl benzene solfonic acid amide, typical aromatic diluters like poly phenyls, dibenzyl toluene, xylyl toluene, dixylyl toluene and polymeric compounds like polyethers, polyesters, polycarbonates, polyolefines can be used. Also low molecular weight alcohols that may contain more than one OH-function like propane-1,2, diol may be used. From the group of polymeric compounds, polypropylene glycols and its derivatives are preferred.

As the additive (E) is an optional component, it may not be present at all, but typically it can be present in the composition at an amount of about 0.1 to about 50 wt.-% or in amount of about 4 to about 35 wt.-% or in amount of about 5 to about 40 wt.-% with respect to the whole composition.

If used as impression material in the dental field the additive(s) can be present in an amount in the range of about 10 to about 65 wt.-%, or in the range of about 25 to about 60 wt.-% with respect to the cured composition.

If used as duplicating material in the dental field the additive(s) can be present in the range of about 10 to about 90 wt.-%, or in the range of about 20 to about 85 wt.-% with respect to the cured composition.

The cured composition of the invention preferably fulfills at least one of the following parameters:

-   -   Shore hardness A (according to DIN 53505) of at least about 40         after 24 h or of at least about 45 or at least about 50 after 24         h.     -   Tensile strength (according to DIN 53504) of at least about 1.6         MPa or of at least about 1.9 MPa or at least about 2 MPa.     -   Elongation at break (according to DIN 53504) of at least about         150% or of at least about 200% or at least about 220%.

The uncured composition of the invention can have a viscosity of at least about 10 Pa*s or of at least about 20 Pa*s or of at least about 40 Pa*s (measured at a shear rate of 95 1/s at 23° C.).

A useful composition according to the invention can comprise

Component (A) in an amount of about 10 wt.-% to about 90 wt.-%, preferably in an amount of about 30 wt.-% to about 80 wt.-% or in an amount of about 40 wt.-% to about 70 wt.-%,

Component (B) in an amount of about 0.1 wt.-% to about 20 wt.-%, preferably in an amount of about 0.5 wt.-% to about 15 wt.-% or in an amount of about 1 wt.-% to about 10 wt.-%,

Component (C) in an amount of about 1 wt.-% to about 30 wt.-%, preferably in an amount of about 2 wt.-% to about 20 wt.-% or in an amount of about 3 wt.-% to about 10 wt.-%,

Component (D) in an amount of about 0 wt.-% to about 80 wt.-%, preferably in an amount of about 5 wt.-% to about 70 wt.-% or in an amount of about 6 wt.-% to about 60 wt.-%,

Component (E) in an amount of about 0 wt.-% to about 50 wt.-%, preferably in an amount of about 5 wt.-% to about 40 wt.-% or in an amount of about 4 wt.-% to about 35 wt.-%, with respect to the whole composition.

The invention also relates to a process of producing a composition as described in the text above comprising the step of mixing component (C) with components (A) and (B), and optionally with components (D) and (E), wherein components (A) to (E) are defined as described the text above.

The invention also relates to a kit of parts comprising

-   -   Part I comprising component (A) and component (B) and optionally         component (D) and/or component (E) and     -   Part II comprising component (C) and optionally component (D)         and/or component (E)         wherein components (A) to (E) are defined as described the text         above.

The curable composition as described above can be used broadly for coating substrates, as sealing material, moulding material, for adhesively fixing substrates and/or making impressions, for modeling of objects or body parts.

The curable composition is especially useful for producing dental materials like precision impression materials, bite registration materials, duplicating materials, modelling materials or situation impression materials.

In this respect, the composition can be used e.g. for making impressions of soft and hard dental tissue. This can simply be achieved, e.g. filling the material into a dental tray and putting the tray into the mouth of a patient.

If used in the dental field, curing is preferably carried out at a temperature below about 50° C. or below about 40° C. or below about 30° C. A useful time range is within about 20 min or within about 10 min after mixing of the components for materials placed in patients mouth and cured (e.g., impression materials) and up to 45 min for materials used in the dental lab (e.g., duplicating materials, modelling materials). In other fields of use (sealing, moulding, coating, adhesively fixing), higher cure temperatures and longer setting times may be employed. Setting times in the range of about 30 min or about 1 hour can still be useful.

The material is regarded as cured, if the cured material fulfils the requirements for its use. E.g. a dental precision impression material typically fulfils the requirements for its use if it fulfils the requirements of ISO 4823:2000 (such as compatibility with gypsum, strain in compression, recovery from deformation, detail reproduction, linear dimensional change).

Especially in the dental field two further parameters might be of some importance: working time and oral setting time.

According to DIN EN ISO 4823:2000 impression materials can be classified as Type 0 (kneadable), Type 1 (high viscosity), Type 2 (medium viscosity), and Type 3 (low viscosity).

The total working time at room temperature (23° C.) measured according to DIN EN ISO 4823:2000 for Impregum™ Garant L DuoSoft and Permadyne™ Garant L 2:1 (3M ESPE AG), both Type 3 regular setting polyether precision impression materials, is 3 min 40 s±15 s and 4 min±15 s, respectively.

The oral setting time is given by the manufacturer in the instructions for use. According to DIN EN ISO 4823:2000 the elastomeric property recovery from deformation of the vulcanized material have to reach values of ≧96.5% within the recommended oral setting time. In addition according to DIN EN ISO 4823:2000 the elastomeric property strain in compression of the vulcanized material has to come up to a value within the range of 0.8 to 20.0% for Type 0 and Type 1 materials and in the range of 2.0 to 20.0% for Type 2 and Type 3 materials, respectively within the recommended oral setting time.

If the composition is to be used as dental impression material, appropriate working times are in a range of about 20 s to about 7 min or about 30 s to about 6 min at room temperature (23° C.). For impression materials oral setting times should be as short as possible. Suitable oral setting times are e.g. about 6 min or about 5 min.

If used in the dental field, the composition can be applied using e.g. the following steps:

-   -   providing the components of the composition,     -   mixing the components,     -   applying the composition to a surface,     -   letting the composition set.

The surface can be the surface of soft or hard oral tissue, the surface of an impression material, preferably of a cured impression material, the surface of a crown or the surface of a model of a tooth stump.

The invention also relates to a method of using of component (B) as described in the text above for increasing the tear strength and/or elongation at break of a polyether groups containing composition. This can be achieved by adding component (B) to the other components of the composition.

EXAMPLES

Objects and advantages of this invention are further illustrated by the following examples, but the particular materials and amounts thereof recited in these examples, as well as other conditions and details, should not be construed to unduly limit this invention. Unless otherwise indicated, all parts and percentages are on a weight basis and all water is deionized water; measurements were conducted under ambient conditions (23° C.). Deviations of the value of the experimentally determined equivalent weight compared to the calculated equivalent weight are due to inaccurate measurements, non quantitative chemical reaction and/or residue of solvents.

Test Methods

Tensile Strength (MPA) and Elongation at Break (%)

Tensile strength and elongation at break were measured according to DIN 53504, form S2. Five independent measurements were performed. A “Universalprüfmaschine Zwick 1435” (Zwick GmbH & Co, Ulm) was used as the measuring device.

Shore Hardness A

Shore Hardness A is a very convenient method to obtain data about the degree of vulcanization. The value of Shore Hardness is a common number in dentistry to characterize a cured impression material. Time dependant measurements were done according to DIN 53505. For determination of the values three independent measurements were performed. A “Handhärteprüfgerät Zwick 3150” (Zwick GmbH & Co, Ulm) was used as the measuring device. The accuracy of the given values is ±1.

Formulations:

The Base Paste and Catalyst Paste used had the following compositions:

Base Paste 1 53.5% difunctional aziridino polyether ((EO (ethylene oxide)/THF (tetra hydro furan) = ratio 1/4; polyether back bone; Mn: 6000); difunctional monomer; obtainable by using the method described in Ex. 40 of U.S. Pat. No. 3,456,242 using 3-ethylene imino butyl amine) 15.7% fat (trisacylic ester of glycerine) 10.4% dibenzyl toluene (Atofina, CAS-No 26898-17-9)   1% surfactant (copolymer of EO/PO); (C. H. Erbslöh KG, CAS-No 9003-11-6)  0.8% imidazole compound; (according to Ex. 2 of EP 0 110 429 B1)  6.5% diatomaceous earth; (Solvadis Specialities GmbH, CAS-No 68855-54-9) 12.1% unreactive polyether ((EO (ethylene oxide)/THF (tetra hydro furan) = ratio 1/4; polyether back bone; Mn: 6000); obtainable by using the method described in Ex. 4 of EP 0 421 371 B1)

Catalyst Paste 1 19.3% sulfonium salt tetrafluoroborate; (obtainable by using the method described in Ex. 41 of U.S. Pat. No. 4,167,618) 40.5% acetyl tributyl citrate (Croda Surfactants Ltd, CAS 77-90-7)  3.5% surfactant (copolymer EO/PO); (C. H. Erbslöh KG, CAS-No 9003-11-6) 24.1% highly dispersed silica, surface treated (HDKH ™, Wacker, CAS-No 68909-20-6) 12.1% diatomaceous earth (Solvadis Specialities GmbH, CAS-No 68855-54-9)  0.5% pigments

Catalyst Paste 1 and the Base Paste 1 were mixed together in a volume ratio of 1:5 (equivalent to the ratio by weight 1.00 g base paste and 0.24 g catalyst paste). The composition was prepared by manually mixing 9.00 g base paste with 2.16 g of catalyst paste using a spatula (Table 1, Entry 0 and Table 2 Entry 0).

Synthesis of Crosslinker Compounds

Crosslinker Compound 1

XAMA™-220 (TTMAP), Trimethylolpropane tris(3-aziridinopropionate), CAS #52234-82-9 is commercially available.

Crosslinker Compound 2

a) Reaction of Polycaprolactone-Monoacrylate with Desmodur N3300

331 g (580.1 mmol) Desmodur N3300 (Bayer AG, NCO-equivalent 190 g/mole), 465.1 mg dibutyl-tin-dilaurate, 186.1 mg 4-methyl-2-tert.butyl phenole, 116.1 ml ethyl acetate were stirred in a reactor at 40° C. 600.6 g (1743.9 mmol) of TONE M 100 (Dow Chemical Company, OHZ=162.9) were added during 3 h while the temperature rose to 53° C. The reaction mixture was stirred overnight at 40° C. until reaction was completed. Product 2a was obtained as a clear, slightly yellow, liquid. The product 2a contained about 12% ethyl acetate and had a C═C equivalent of 573 g/mole.

b) Aziridino-Derivative of a Trifunctional Caprolactone-Acrylate

114.6 g of Product 2a (0.2 equivalent based on C═C) were placed into a round bottom flask at 23° C. 17.13 g 2-methylaziridine (0.30 mole) were added carefully under stirring within 1 h while the temperature was kept below 30° C. using external cooling. After 2 h stirring at room temperature the reaction mixture was stirred for additional 16 h at 23° C. to complete the reaction. After removing excess of 2-methylaziridine under vacuum 108.7 g of a clear colourless liquid Product 2 remained. Product 2 showed no remaining acrylate or 2-methylaziridine in the ¹H-NMR spectrum; aziridino-equivalent 600 g/mole; Viscosity: 42 Pa*s.

Crosslinker Compound 3

22.8 g of dipentaerythritol-pentaacrylate (0.2 equivalent of C═C; viscosity: 14.5 Pa*s, Fa. Dajac) were placed into a round bottom flask at 23° C. 12.56 g 2-methylaziridine (0.22 mole) were added carefully under stirring within 1 h while the temperature was kept below 40° C. using external cooling. After 2 h stirring at room temperature the reaction mixture was stirred for additional 2 h at 45° C. to complete the reaction. After removing excess of 2-methylaziridine under vacuum 32.2 g of clear colourless liquid Product 3 remained. Product 3 showed only traces of remaining acrylate in the ¹H-NMR spectrum; Viscosity: 7.2 Pa*s.

Crosslinker Compound 4

30.6 g of trimethylolepropane-triacrylate (0.2 equivalent of C═C; Fa. Erbslöh) were placed into a round bottom flask at 23° C. 12.56 g 2-methylaziridine (0.22 mole) were added carefully under stirring within 1 h while the temperature was kept below 40° C. using external cooling. After 2 h stirring at room temperature the reaction mixture was stirred for additional 2 h at 45° C. to complete the reaction. After removing excess of 2-methylaziridine under vacuum 40 g of clear colourless liquid product 4 remained. Product 4 showed only traces of remaining acrylate in the ¹H-NMR spectrum; aziridino-equivalent 223 g/mole; Viscosity: 0.18 Pa*s.

Reference—Crosslinker Compound 5* (without 2-Alkyl Substituted Aziridino Groups)

99.36 g ethoxylated pentaerythritol (0.5 Equivalent OH, 15 Mole EO per pentaerythritol molecule, Aldrich) were dissolved in the same amount of toluene. This solution was added to a stirred suspension of 81.08 g carbonyldiimidazole (CDI) (0.5 mole, purity ˜97%, FLUKA) at 37° C. in 11 toluene within 45 minutes. After additional 12 hours of stirring at 37° C. the turpid reaction mixture was cooled to 23° C. 62.8 g 3-(ethylenimino)-butylamin (0.55 mole, boiling point.: 50° C./10 Torr, ρ=0.8780 g/ml) (made from 3-(ethylenimino)-butyronitrile (CAS: 4078-19-7 by hydrogenation) were added in one portion and the reaction mixture was stirred at 23° C. for another 48 h. The reaction mixture was filtrated, evaporated from the solvent and imidazole was stripped of by repeated thin film evaporation. Product 5* was obtained as a clear viscous liquid of 43 Pa*s and an aziridino-equivalent of 486 g/mole.

Adding Different Highly Functional Crosslinkers to the Formulation

In the following experiments parts of dibenzyl toluene (CAS-No 26898-17-9) in Base Paste 1 were exchanged against the respective crosslinker compounds. The formulas of the crosslinker compounds used are as shown above.

Whereas in the Base Paste 1 the concentration of aziridino groups was about 1.73*10⁻² mol per 100 g in all of the altered formulation the concentration of aziridino groups was attuned to 2.51*10⁻² mol per 100 g base paste by exchanging dibenzyl toluene by the same amount of cross-linker.

The amount of imidazole compound was adjusted in the same way to keep an approximate molar ratio of aziridine groups:imidazole compound of about 1.00 to about 0.1.

To assure that in all experiments the same molar ratio of aziridino groups:sulfonium salt tetrafluoroborate was used, the amount of sulfonium salt tetrafluoroborate in Catalyst Paste 1 was adapted to 28.0 g by exchanging 8.7 g acetyl tributyl citrate by the same amount of sulfonium salt tetrafluoroborate. The altered Base Pastes were reacted with the altered Catalyst Pastes.

Table 1 and Table 2 describe the effect the addition of crosslinkers has on the value of Shore Hardness A during vulcanization and on the value of tear strength and elongation at break. The naming of the crosslinker as 1, 2, 3, . . . corresponds to the numbering of the crosslinkers in the text above in regard to formulas.

TABLE 1 Aziridino Used monomers groups in Amount 100 g Cross Amount difunctional base Shore-Hardness A after Entry linker cross-linker prepolymer paste 8 min 10 min 15 min 30 min 24 h 0 — — 53.5% 1.73 10⁻² mol 27 33 40 46 50 1 1 1.36% 53.5% 2.51 10⁻² mol 31 38 46 51 54 2 2 4.70% 53.5% 2.51 10⁻² mol 27 32 40 47 52 3 3 1.68% 53.5% 2.51 10⁻² mol 26 33 40 47 52 4 4 1.75% 53.5% 2.51 10⁻² mol 27 32 43 49 52 5  5* 8.23% 53.5% 2.51 10⁻² mol 39 44 48 52 54

TABLE 2 Aziridino Used monomers groups in Amount 100 g Tensile Elongation at Cross Amount difunctional base Strength break Entry linker cross-linker prepolymer paste [MPa] [%] 0 — — 53.5% 1.73 10⁻² mol 1.73 10⁻² mol  1.61 ± 0.20 1 1 1.36% 53.5% 2.51 10⁻² mol 2.35 ± 0.08 256 ± 14 2 2 4.70% 53.5% 2.51 10⁻² mol 1.96 ± 0.22 230 ± 39 3 3 1.68% 53.5% 2.51 10⁻² mol 2.68 ± 0.22 214 ± 25 4 4 1.75% 53.5% 2.51 10⁻² mol 2.28 ± 0.11 266 ± 20 5  5* 8.23% 53.5% 2.51 10⁻² mol 1.99 ± 0.23 200 ± 37 

1. A composition comprising a) a prepolymer as component (A), wherein the prepolymer comprises aziridino groups, but not silicone moieties, and is characterized by an equivalent weight EW1, b) a crosslinker as component (B), wherein the crosslinker has a molecular structure being different from the molecular structure of the prepolymer and comprises at least three 2-alkyl-substituted aziridino groups and is characterized by an equivalent weight EW2, and c) an initiator as component (C) being able to start curing of the composition, wherein equivalent weight is defined as the molecular mass of the molecule divided by the number of aziridino groups present in the molecule, and wherein EW1>EW2.
 2. The composition of claim 1, further comprises a filler as component (D).
 3. The composition of claim 2, further comprising an additive as component (E).
 4. The composition according to claim 1, wherein the prepolymer has a molecular weight (Mn) within the range of about 3,000 to about 12,000 and the crosslinker has a molecular weight (Mn) within the range of about 400 to about 5,000.
 5. The composition according to claim 1, wherein the composition satisfies at least one of the following parameters after curing: a) a shore hardness A (DIN 53505) of at least 40 after 24 h, b) a tensile strength (DIN 53504) of at least 1.6 MPa, and/or c) an elongation at break (DIN 53504) of at least 180%.
 6. The composition according to claim 3 comprising a) Component (A) in an amount of about 10 wt.-% to about 90 wt.-%, b) Component (B) in an amount of about 0.1 wt.-% to about 20 wt.-%, c) Component (C) in an amount of about 1 wt.-% to about 30 wt.-%, d) Component (D) in an amount of about 0 wt.-% to about 80 wt.-%, e) Component (E) in an amount of about 0 wt.-% to about 50 wt.-% with respect to the whole composition.
 7. The composition according to claim 1, wherein the prepolymer is characterized by at least one of the following features: a) a molecular weight (Mn) in the range of about 3,000 to about 30,000, b) a linear molecular structure of the backbone, c) at least about 2 aziridino groups, and/or d) an equivalent weight (EW1) of at least
 1000. 8. The composition according to claim 1, wherein the prepolymer comprises polyether, polyurethane and/or polyester groups.
 9. The composition according to claim 1, wherein the crosslinker is characterized by at least one of the following features: a) a molecular weight (Mn) in the range of about 200 to about 10,000 b) a branched molecular structure of the backbone, c) at least three 2-alkyl-substituted aziridino groups; and/or d) an equivalent weight (EW2) of about
 100. 10. The composition according to claim 1, wherein the crosslinker has one of the following structures:


11. The composition according to claim 2, wherein component (D) comprises one or more fillers selected from the group consisting of reinforcing and non-reinforcing fillers.
 12. The composition according to claim 3, wherein component (E) comprises one or more additives selected from the group consisting of dyes, pigments, thixotropic agents, flow improvers, polymeric thickeners, surfactants, odorous substances, diluting agents and flavourings. 